Adding function composition

Author: jnape

src/main/java/com/jnape/palatable/lambda/MonadicFunction.java

@@ -1,5 +1,16 @@
 package com.jnape.palatable.lambda;
 
 public abstract class MonadicFunction<A, B> {
+
     public abstract B apply(A a);
+
+    public final <C> MonadicFunction<A, C> then(final MonadicFunction<B, C> f) {
+        return new MonadicFunction<A, C>() {
+            @Override
+            public C apply(A a) {
+                MonadicFunction<A, B> g = MonadicFunction.this;
+                return f.apply(g.apply(a));
+            }
+        };
+    }
 }

src/test/java/com/jnape/palatable/lambda/MonadicFunctionTest.java

@@ -0,0 +1,27 @@
+package com.jnape.palatable.lambda;
+
+import org.junit.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+
+public class MonadicFunctionTest {
+
+    @Test
+    public void composesByApplyingFunctionThenForwardingToNextFunction() {
+        MonadicFunction<Integer, Integer> add2 = new MonadicFunction<Integer, Integer>() {
+            @Override
+            public Integer apply(Integer integer) {
+                return integer + 2;
+            }
+        };
+        MonadicFunction<Integer, String> toString = new MonadicFunction<Integer, String>() {
+            @Override
+            public String apply(Integer integer) {
+                return integer.toString();
+            }
+        };
+
+        assertThat(add2.then(toString).apply(2), is(toString.apply(add2.apply(2))));
+    }
+}